Method of making a dental mill blank and support stub assembly

ABSTRACT

A mill blank assembly for making a dental prosthesis includes a milling section and a support section. The support section is adapted to fit in a chuck or collet of a milling machine. One of the milling section and the support section includes a projection that extends into a recess of the other, in order to enhance the strength of the bond between the milling section and the support section. As a result, the completed assembly is less likely to fracture or become disassembled during the milling process.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention broadly relates to a mill blank assembly used in thefield of dentistry to create an inlay, onlay, crown, veneer, coping,bridge, bridge framework, implant, implant abutment or other restorationor restoration component. More specifically, the present invention isdirected to a mill blank assembly that is especially adapted for usewith computer-aided design and machining processes to create a dentalprosthesis.

2. Description of the Related Art

A variety of dental procedures are known for replacing or repairingdamaged, weakened or missing tooth structures. For example, a dentalprosthesis commonly known as a filling is often used to fill cavities inteeth caused by tooth decay or caries. Somewhat larger prosthetics alsoused to fill cavities are known as inlays and onlays. Fillings, inlaysand onlays may also be utilized to restore the shape of teeth that havebeen chipped or broken.

Other types of dental prosthetics include bridges, full crowns andpartial crowns. Typically, these prosthetics are much larger thanfillings and as a result are often more visible in the oral cavity. Fulland partial crowns may be supported by remaining portions of theoriginal tooth structure and/or by a post extending toward the bonyregion of the jaw. Bridges, on the other hand, are structures thatconnect to adjacent tooth structure and provide an artificial tooth ortooth crown to replace corresponding, missing structure.

In the past, fillings and some inlays and onlays were often made of asilver-colored metal alloy known as amalgam due to its relatively longlife and relatively low cost. Another advantage offered by amalgam isthat it allows a dental practitioner to fit and fabricate therestoration during a single session with a patient. Unfortunately,amalgam is not considered aesthetic since its silver color sharplycontrasts to the appearance of natural teeth in the oral cavity.

Another material used for dental prosthetics, and particularly forlarger inlays and fillings, is gold. However, like amalgam, the color ofgold sharply contrasts with the appearance of natural teeth and ishighly visible in the oral cavity. In addition, gold is relativelyexpensive in comparison to other dental materials.

As a consequence, many dental practitioners are increasingly turning toceramic or polymer-ceramic composite materials for use to make dentalprosthetics. Dental ceramic materials and dental polymer-ceramiccomposite materials can provide an appearance that closely matches theappearance of natural teeth. Such materials are also available invarious color shades so that the practitioner can select a color thatclosely matches the color of adjacent tooth structure.

Dental polymer-ceramic composite materials for use as restoratives areavailable from various manufacturers in paste-type form. Such materialsare often supplied in capsules that are releasably received in areceptacle of a hand-held dispenser. The dispenser typically includes alever that, when depressed, extrudes a quantity of the material from thecapsule and directly onto the tooth structure. The material includes apolymerization initiator that serves to harden the material once it hasbeen placed on the tooth structure and shaped by the practitioner toresemble natural tooth structure.

A variety of techniques may be employed to help shape the unhardenedrestorative paste to a desired configuration once dispensed onto thepatient's tooth structure. For example, if the material is used to filla relatively small cavity, the material can be dispensed directly intothe cavity and then shaped by hand. A hand instrument such as a dentalpick is used to help pack the material in the cavity and to blend theexternal surface of the paste with adjacent, external portions of thepatient's tooth. As another example, if a portion of one or more sidesof a tooth is to be restored, the practitioner may elect to use a matrixband or sectional matrix band next to the tooth structure to help holdthe material in place while it hardens. The matrix band or sectionalmatrix band serves as a formwork, similar to formwork used in concrete,to help hold the material in place and also to help define an outersurface of the composite material while it hardens.

However, larger prosthetics are often fabricated outside of the oralcavity and then placed in the patient's oral cavity once completed. Forthese types of prosthetics, an impression is often taken of thepatient's tooth structure of interest along with adjacent regions of thegingiva, using an elastomeric impression material that provides anegative physical image of the tooth structure and gingival region.Next, a cast positive model is made by pouring a quantity of plaster ofParis into the impression and allowing the plaster of Paris to harden.The resulting plaster of Paris or “stone” model is then used in thelaboratory to make a prosthetic that is ultimately transferred to thepatient's oral cavity.

The laboratory procedure for making the prosthetic may be somewhatinvolved, depending on the type of prosthetic that is needed. In onemethod, for example, a wax replica of the desired crown is built on thestone model. The wax replica is then embedded in a refractory investmentmaterial and fired to create another negative physical image of the oralstructure of interest. Porcelain is then forced into the investmentmaterial under pressure and heat in order to make the crown.

However, a number of disadvantages arise when the foregoing procedure isfollowed to make a crown. In such a procedure, the patient typicallytravels to the practitioner's office two times: a first time to enablean impression to be taken, and a second time a few days later after thestone model has been made and the crown has been fabricated in thedental laboratory. Moreover, if the completed crown must be returned tothe laboratory because its shape, fit or appearance is not satisfactory,the patient is often then required to return to the dental office for athird visit. In many dental practices, the crown is not made in alaboratory that is part of the office but is instead sent to a centrallaboratory in another area of the town or region.

Furthermore, the fabrication of custom dental crowns and otherprosthetics by hand from stone models is an art that involves a highdegree of skill and craftsmanship, as well as intensive labor. Moreover,prosthetics that are placed in the anterior regions of the patient'soral cavity are often highly visible. It is widely considered difficultto make a porcelain prosthetic that exactly matches the translucency andcolor of natural teeth.

Recently, increased interest has been directed toward the use ofcomputer automated machinery for fabricating dental prosthetics, usingfar less labor than prior methods such as the method for making a crowndescribed above. For example, several systems are known for collecting aset of electronic data that is representative of the patient's toothstructure of interest. The data is then used by an automated mechanicalmilling machine (such as computer-aided milling machine) to fabricate aprosthetic that, when completed, closely matches the shape of naturaltooth structure.

Examples of computer-aided milling machines used in the field ofdentistry include the CEREC 2™ and CEREC 3™ machines available fromSirona Dental Systems of Bensheim, Germany, the VITA CELAY™ machine fromVita Zahn Fabrik of Bad Sackingen, Germany, PRO-CAM™ from Intra-TechDental Products, of Dallas, Tex. and PROCERA ALL CERAM™ from NobelBiocare USA of Westmont, Ill. U.S. Pat. Nos. 4,837,732, 4,776,704 and4,575,805, as well as PCT patent application No. WO 96/37163 alsodisclose systems for making dental prosthetics using computer-aidedmilling machines.

The fabrication of a dental prosthesis using a computer-aided machiningsystem typically involves the use of a “mill blank”, a block of materialfrom which the prosthetic is cut. Dental mill blocks are often made of aceramic material. Commercially available dental mill blanks include VITACELAY™ porcelain blanks from Vita Zahn Fabrik, VITA NCERAM™ ceramicblanks from Vita Zahn Fabrik, MACOR™ micaceous ceramic blanks fromCorning, and DICOR™ micaceous ceramic blanks from Dentsply. A dentalmill blank made of a ceramic silica material as described in U.S. Pat.No. 4,615,678. An improved ceramic dental mill blank is described inapplicant's co-pending application entitled “CERAMIC DENTAL MILLBLANKS”, U.S. Ser. No. 09/383,560, filed Aug. 26, 1999.

Dental mill blanks may also be made of resinous materials. An example ofa dental mill blank made of a polymeric resin and a filler is describedin applicant's co-pending U.S. patent application entitled “DENTAL MILLBLANKS”, U.S. Ser. No. 09/227,230, filed Jan. 8, 1999. Dental millblanks made of such material exhibit superior milling characteristicssuch as hardness and cutting properties relative to previously knowndental mill blanks.

Many commercially available dental mill blanks are made of a two-piececonstruction that comprises a support stub section and a milling blanksection. The support section is cylindrical and adapted to fit into acollet or a Jacobs chuck of a milling machine. Often, the supportsection is made of metal, since the support section is ultimatelydetached from the milling section and does not form part of the finishedprosthetic. The support section is typically made of a relatively softmetallic material such as an aluminum alloy that is easy to machine toprecise tolerances.

The milling section of conventional two-piece dental mill blankassemblies is often made of one of the aesthetically-pleasingrestorative materials described above so that the resulting prostheticprovides a natural appearance once placed in the oral cavity. Themilling section has a flat face that is joined to a flat face of thesupport section by an adhesive. An example of one type of two-piececonstruction is described in U.S. Pat. No. 4,615,678.

It has been observed, however, that dental mill blank assembliesoccasionally fracture during the milling process. In some instances, thefracture occurs in the joint between the support stub section and themilling section. It is suspected that lateral forces exerted by themilling tool on the milling section create a shear force that exceedsthe strength of the adhesive bond of the joint.

Unfortunately, if the milling section has broken away from the supportsection before the milling process has been completed, the mill blankassembly must be discarded and replaced with a new assembly.Consequently, the fracture of dental mill blank assemblies represents atime-wasting nuisance to the personnel operating the milling system.Replacement of the dental mill blank assembly with a new assembly alsorepresents an additional cost to the dental laboratory, the dentalpractitioner and the patient that is best avoided if at all possible.

SUMMARY OF THE INVENTION

The present invention is directed toward a dental mill blank assemblythat presents an enhanced resistance to fracture during the time thatthe mill blank assembly is machined in a milling system. The mill blankassembly is especially adapted to safely resist forces exerted by amilling tool in lateral directions so that the dental prosthetic can bemilled to completion. As a result, unintentional detachment of thesupport section from the milling section is avoided.

In more detail, the present invention in one aspect is directed toward amill blank assembly for a dental prosthesis, and comprises a millingsection made of a material suitable for making a dental prosthesis. Themill blank assembly also comprises a support section having a shaft forreleasably supporting the mill blank assembly in a milling machine. Thesupport section is fixed to the milling section and is made of amaterial different than the material of the milling section. One of themilling section and the support section includes a projection, and theother of the milling section and the support section includes a recessthat receives the projection.

A number of additional features are also possible. For example, the millblank assembly may include an additional one or more projections, eachof which is received in an additional, respective recess. Theprojections and the recesses may have closely complementalcross-sectional configurations that present a precise mating fit.Additionally, an adhesive may be provided to enhance the bond betweenthe support section and the milling section.

Another aspect of the present invention is directed toward making adental mill blank assembly. The method comprises the acts of providing amold having an inlet channel and a mold cavity in communication with theinlet channel, and directing a quantity of restorative material along apath that leads through the channel and into the mold cavity. The methodalso includes the act of hardening restorative material located in themold cavity as well as restorative material located in the channel. Themethod further includes the acts of removing the hardened restorativematerial from the mold cavity and the channel, and coupling the hardenedrestorative material to a support section. The act of coupling thehardened restorative material to a support section includes the act ofinserting a portion of the hardened restorative material that wasformerly in the channel into a recess of the support section.

These and other features of the invention are described in detail belowand are illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded, perspective view of a mill blank assembly for adental prosthesis according to one embodiment of the invention, andshowing a milling section and a support section as they appear beforebeing assembled together;

FIG. 2 is a view somewhat similar to FIG. 1 but shown from a somewhatdifferent direction;

FIG. 3 is a view somewhat similar to FIG. 2 except that the millingsection and the support section have been assembled together;

FIG. 4 is an enlarged, fragmentary, side cross-sectional view of aportion of the dental mill blank assembly shown in FIG. 3;

FIG. 5 is an exploded view of a mold assembly that is especially adaptedfor use in making the dental mill blank assembly depicted in FIGS. 1-4;and

FIG. 6 is a fragmentary perspective view of the mold assembly shown inFIG. 5, except that the mold assembly components are shown as assembledtogether, wherein an outer mold component has been cut away to reveal amold cavity, and wherein a dental restorative material has been placedin the mold cavity to make the milling section of the dental mill blankassembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A mill blank assembly for a dental prosthesis according to oneembodiment of the invention is illustrated in FIGS. 1-4 and is broadlydesignated by the numeral 10. The mill blank assembly includes a stub orsupport section 12 and a mill blank or milling section 14 that is fixedto the support section 12.

The support section 12 includes a shaft 16 having a longitudinal axis.Preferably, the shaft 16 has an overall cylindrical shape, althoughother shapes are also possible. For example, the shaft 16 could have ahexagonal shape or an octagonal shape in reference planes perpendicularto its central, longitudinal axis. Preferably, an outer end of the shaft16 is chamfered to facilitate insertion of the assembly 10 into a colletor a chuck of a milling machine.

The support section 12 also includes a flange 18 that is connected to anend of the shaft 16 that is opposite the chamfered end. The flange 18 asshown in the drawings also has a cylindrical shape, but has a diametersomewhat larger than the diameter of the shaft 16. Preferably, thecentral axis of the flange 18 is collinear with the central axis of theshaft 16, and presents a flat, outwardly facing bonding surface 20having an annular configuration.

However, the flange 18 may have shapes other than cylindrical. Forexample, the flange 18 may have an overall square, hexagonal oroctagonal shape in reference planes perpendicular to its central axis.Moreover, the central axis of the flange 18 may be laterally offset fromthe central axis of the shaft 16 if desired.

Preferably, the flange 18 also includes a notch 22 for receiving anindexing pin of a milling machine. As shown in the drawings, the notch22 extends along the outer cylindrical wall of the flange 18, andextends inwardly toward the central axis of the flange. Optionally, butnot necessarily, the notch 22 has a curved inner wall such that thenotch 22 presents an overall, generally “U”-shaped configuration whenlooking in a direction along the central axis of the shaft 16.

The support section 12 may also have other features that align orenhance the coupling between the milling machine and the assembly 10.For example, the shaft 16 could have a recess or a groove that extendsabout its circumference to receive a setscrew or other structure of thecollet or chuck. Other types of alignment or coupling-enhancing featuresare also possible, depending on the milling machine(s) selected.

Optionally, all or a portion of the outer cylindrical wall of the flange18 provides a calibration surface for use during the milling process toestablish tool wear. Although the calibration surface in this embodimenthas the shape of a cylinder or partial cylinder, other shapes are alsopossible. The calibration surface may be located next to the notch 22 oralternatively may be located on the peripheral wall in an area oppositethe notch 22 relative to the central axis of the flange 18.

If a calibration surface is provided, it is preferred that thecalibration surface is manufactured to be located a precise distance,within very precise dimensional tolerances, from the central axis of theflange 18. The dimensional tolerance is preferably plus or minus 0.1 mm,more preferably is plus or minus 0.05 mm and most preferably is plus orminus 0.01 mm.

The calibration surface is used by a milling machine, typically beforethe milling process begins, as a reference surface to accuratelydetermine the overall dimension (such as the length) of the millingtool. As an example, the milling machine may rotate the tool whileslowly moving the tool toward the calibration surface. The millingmachine has a speed sensor for detecting the rotational speed of thetool and a positional sensor for tracking the axial position of thetool. The rotational speed of the tool slightly decreases as soon as thetool contacts the calibration surface. The machine is programmed todetermine the overall length of the tool and compensate for tool wear bydetermining the axial position of the tool (i.e., the distance from thecentral axis of the flange 18) in relation to the calibration surface assoon as a decrease in the rotational speed is detected. Other methods touse the calibration surface as a reference surface are also possible,such as methods that employ laser sighting techniques.

The support section 12 also has a recess 24 that is located in theflange 18. In the illustrated embodiment, the recess 24 has an overallgenerally cylindrical shape with a central axis that is collinear withthe central axis of the flange 18 and the central axis of the shaft 16.As a consequence, the recess 24 is located in this embodiment in thecenter of the bonding surface 20. The inner end of the recess 24 has agenerally dome-shaped configuration.

However, the recess 24 may alternatively have other shapes and belocated in offset relation to the central axis of the flange 18. Forexample, the recess 24 may have a square, rectangular, oval or othershape in reference planes perpendicular to the central axis of theflange 18. Optionally, the recess 24 may have a length sufficient toextend into the adjacent end portion of the shaft 16.

The milling section 14 includes a main body 26 as well as a projection28 that is connected to the main body 26. Preferably, the body 26 andthe projection 28 are integrally joined together and form part of asingle, unitary body. In the embodiment shown in the drawings, the body26 has an overall cylindrical shape, although other shapes are alsopossible.

For example, the milling section 14 may have a shape in reference planesperpendicular to its central axis that is rectangular, square, hexagonalor other types of polygons or non-polygons including oval. Preferably,but not necessarily, the central axis of the body 26 is collinear withthe central axis of the projection 28. The body 26 as shown has adiameter that is smaller than the diameter of the flange 18, but asanother option could have a diameter or shape larger than the diameteror shape of the flange 18 if desired.

Preferably, the projection 28 has a cross-sectional configuration inreference planes perpendicular to its central axis that is closelycomplemental to the cross-sectional configuration of the recess 24. As aconsequence, the projection 28 matingly fits in the recess 24 when thesupport section 12 and the milling section 14 are assembled together.Preferably, but not necessarily, the central axis of the body 26 and theprojection 28 are collinear with the central axis of the flange 18 andthe shaft 16 when the support section 12 is assembled to the millingsection 14.

Preferably, the recess 24 has a length in directions along its centralaxis that is somewhat longer than the length of the projection 28. As aconsequence, when the support section 12 is assembled to the millingsection 14, the bonding surface 20 tightly contacts an annular flatbonding surface 30 of the milling section 14 that surrounds theprojection 28. The extra depth provided in the recess 24 ensures thatthe bonding surfaces 20, 30 will fully meet even in instances where thelength of the projection 28 is somewhat larger than expected.

Optionally, the cross-sectional configuration of the projection 28 isslightly larger than the cross-sectional configuration of the recess 24in reference planes perpendicular to the central axis of the assembly 10so that an interference fit is presented. In that instance, theprojection 28 is forced under pressure into the recess 24 in order toestablish a secure press-fit relationship when the support section 12 isassembled to the milling section 14.

Preferably, an adhesive is provided to enhance the bond between thesupport section 12 and the milling section 14. Preferably, the adhesiveextends between the entire area of the bonding surfaces 20, 30, as wellas along the entire cylindrical surfaces of the projection 28 and therecess 24 that are in contact with each other. The adhesive may be anysuitable material that is effective in bonding the sections 12, 14together, such as cyanoacrylate, epoxy, urethane or acrylate.

The milling section 14 is made from a material that is suitable for usein the oral cavity as a dental prosthetic and is also capable of beingmilled in a milling machine without undue hindrance or tool wear.Examples of suitable materials include ceramics, polymers,polymer-ceramic materials and metals.

Examples of suitable metals include stainless steel, alloys of gold ortitanium, nickel-based alloys, cobalt-based alloys or any other alloysuitable for use in the oral environment. Examples of suitable alloys,palladium-based alloys, include those marketed under the tradenamesRexillium™III, Jeneric/Pentron, Inc., Wallingford, Conn.; Degudent™H,Degussa Corporation, South Plainfield, N.J.; Paladent™B, Jeneric/PentronInc., Wallingford, Conn.; Rexillium™ NBF, Jeneric/Pentron, Inc.,Wallingford, Conn. and Allvac™-6-4, Teledyne Allvac, Monroe, N.C.

Examples of suitable ceramic materials include glasses, monocrystallineand polycrystalline ceramics, and glasses with crystalline phases.Polycrystalline ceramics include nanocrystalline materials and may besingle phase or multiphase. Preferred crystalline ceramic materialsinclude aluminum oxide, magnesium-aluminum spinel (MgAl₂O₄), zirconiumoxide, yttrium aluminum garnet, zirconium silicate, yttrium oxide andmullite. Preferred glass containing materials include feld-pathicporcelains; glasses containing crystalline; phases such as mica,leucite, canasite, alumina, zirconia, spinel, hydroxyapatite; andamorphous glasses such as Pyrex™, Vycor™, (both from Corning, Inc.,Corning, N.Y.). Preferred ceramics include those marketed under thetradenames In-Ceram™, (Vita Zahnfabnik, Bad Säckingen, Germany), MarkII™, (Vita Zahnfabnik, Bad Säckingen, Germany), ProCAD™, (Ivoclar AG,Schaan, Lichtenstein), Empress™ (Ivoclar AG, Schaan, Lichtenstein),Empress 2™ (Ivoclar AG, Schaan, Lichtenstein), MACOR™, (Coming Inc.,Coming, N.Y.), DICOR™, (Dentsply International, York, Pa.), Denzir™,(Dentronic AB, Shelleftea, Sweden), Prozyr™, (Norton Desmarquest,Vincennes Cedex, France), Lucalox™, (General Electric, Richmond Heights,Ohio), Bioglass™, (U.S. Biomaterials Corp., Hachua, Fla.), Cerabone A/W,(Nippon Electric Glass, Shiga, Japan), Transtar TPA (Ceradyne, Inc.,Costa Mesa, Calif.), AD-998 (Coors Ceramics, Golden, Colo.), and 998(Vesuvius McDanel, Pa.).

The ceramic milling section may be provided either in a fully denseform, with little or no porosity, or in a porous, partially fired form.If the ceramic mill blank is porous, it may be fired to a fully densestate after milling. Alternatively, the porous ceramic mill blank may beinfiltrated with, for example, a molten glass or a resin that is thenhardened after infiltration.

Preferably, the ceramic material transmits light in the visiblewavelengths in order to provide an aesthetically pleasing appearanceonce milled into a prosthetic and placed in the oral cavity. Preferably,the ceramic material is essentially colorless; i.e., it neither adds norsubtracts color to the light passing through the material to anyappreciable extent. Optionally, however, colorants may be added toachieve desired shades that mimic the color of natural teeth that may beobserved in certain patients.

Preferably, the ceramic mill blanks according to the invention and theresulting prosthetics have a Contrast Ratio value less than about 0.7,preferably less than about 0.6, and more preferably less than about 0.5.The Contrast Ratio value can be determined by following the techniquedescribed in Section 3.2.1 of ASTM-D2805-95, modified for samples ofabout 1 mm thick. The Contrast Ratio value is an indication of the levelof light transmissivity possessed by the milling section 14 and theresulting prosthesis.

Further details regarding preferred ceramic dental mill blank materialsand manufacturing methods for those materials, including informationconcerning modification of the Contrast Ratio described above, are setout in applicant's co-pending U.S. patent application entitled “CERAMICDENTAL MILL BLANKS”, U.S. Ser. No. 09/383,560, which is expresslyincorporated by reference herein.

Preferred polymer-ceramic composite materials for the milling section 14include polymerizable resins having sufficient strength, hydrolyticstability, and non-toxicity to render it suitable for use in the oralenvironment. Preferably, the resin is made from a material comprising afree radically curable monomer, oligomer, or polymer, or a cationicallycurable monomer, oligomer or polymer. Alternatively, the resin may bemade from a material comprising a monomer, oligomer or polymercomprising a free radically curable functionality and a cationicallycurable functionality. Suitable resins include epoxies, methacrylates,acrylates and vinyl ethers.

Polymers for the polymer-ceramic composite milling section 14 includethermoplastic and thermosetting polymers. Suitable thermoplasticpolymers include polycarbonates, nylon, polyetheretherkitone,polyurethanes, polyimides and polyamides. The polymer material may befilled with one or more types of ceramic filler as described below.

The polymer-ceramic composite material also includes an initiator forinitiating polymerization of the material. For example, one class ofuseful initiators includes those capable of initiating both free radicaland cationic polymerization. Preferred free radical polymerizationsystems contain three components: an onium salt, a sensitizer and a freeradical donor. Optionally, the sensitizer may be a visible lightsensitizer that is capable of absorbing light having wavelengths in therange from about 3 nanometers to about 1000 nanometers. If the resin inthe polymer-ceramic composite is not sufficiently hardened beforemilling, further hardening can be carried out after milling and beforeuse in the oral cavity.

Preferably, the polymer-ceramic composite material also includes afiller. The filler is preferably a finely divided material that mayoptionally have an organic coating. Suitable coatings include silane orencapsulation in a polymeric matrix. The filler may be selected from oneor more of many materials suitable for incorporation in compositionsused for medical or dental applications, such as fillers currently usedin dental restorative compositions and the like.

Suitable fillers include zirconia-silica, baria-silica glass, silica,quartz, colloidalsilica, fumed silica, ceramic fibers, ceramic whiskers,calcium phosphate, fluoroaluminosilicate glass and rare-earth fluorides.Suitable fillers also include nanosize heavy metal oxide particles suchas described in applicant's co-pending patent application entitled“RADIOPAQUE DENTAL MATERIALS WITH NANO-SIZED PARTICLES”; U.S. Ser. No.09/429,185 filed Oct. 28, 1999, which is expressly incorporated byreference herein. Other suitable fillers are described in applicant'sco-pending patent applications entitled “CLUSTERED PARTICLE DENTALFILLERS” (U.S. Ser. No. 09/428,830 filed Oct. 28, 1999) and “DENTALMATERIALS WITH NANO-SIZED SILICA PARTICLES” (U.S. Ser. No. 09/428,937filed Oct. 28, 1999), both of which are expressly incorporated byreference herein. Additional suitable fillers are described in U.S. Pat.No. 4,503,169, and applicant's co-pending patent application entitled“RADIOPAQUE CATIONICALLY POLYMERIZABLE COMPOSITINS COMPRISING ARADIOPAQUE FILLER, AND METHOD FOR POLYMERIZING SAME” (U.S. Ser. No.09/168,051 filed Oct. 7, 1998), both of which are incorporated byreference herein. The fillers may be in any morphology, includingspheres, platelets, whiskers, needles, fibers, ovoids, etc. or anycombination of the foregoing.

Further information regarding preferred polymer-ceramic compositematerials, including details of suitable compositions and method ofmanufacturing those materials, are set out in applicant's co-pendingU.S. patent application entitled “DENTAL MILL BLANKS”, U.S. Ser. No.09/227,230, which is also expressly incorporated by reference herein.

The milling section 14 is suitable for fabricating into a variety ofrestorations, including inlays, onlays, crowns, veneers, bridges,implant abutments, copings and bridge frameworks. Various means ofmachining the milling section 14 may be employed to create custom-fitdental prosthesis having a desired shape. It is preferable that theprosthesis be milled quickly without imparting undue damage. Preferably,the prosthesis is milled by computer controlled milling equipment, suchas machines sold under the tradenames Sirona CEREC 2, Sirona CERAC 3,Dentronics DECIM or CadCam Ventures PROCAM.

By using a CAD/CAM milling device, the prosthesis can be fabricatedefficiently and with precision. During milling, the contact area may bedry, or it may be flushed with or immersed in a lubricant.Alternatively, it may be flushed with an air or gas stream. Suitableliquid lubricants are well known, and include water, oils, glycerine,ethylene glycols, and silicones. After milling, some degree offinishing, polishing and adjustment may be necessary to obtain a customfit in to the mouth and/or aesthetic appearance.

The support section 12 is made of a material that can be manufactured torelatively precise tolerances and has sufficient strength for supportingthe assembly in a collet or chuck of a milling machine. An example of asuitable material is aluminum. Optionally, the aluminum may be platedwith gold chromate in order to enhance the bond between the supportsection 12 and the adhesive.

As another option, the support section 12 may be made of an aluminumwhich has been anodized. It has been found that an anodized surface isvery effective in enhancing the bond between the support section 12 andthe adhesive. A black anodized surface is presently preferred.

One method of making the mill blank assembly 10 shown in FIGS. 1-4 isillustrated in FIGS. 5 and 6. In FIGS. 5 and 6, a mold or mold assembly36 includes a male first or inner component 38 and a female second orouter component 40. Optionally, the first and second components 38, 40are made of a relatively inexpensive material such as injection-moldedplastics. Suitable materials for the components 38,40 include acrylics(such as polymethylmethacryate (“PMMA”)), polycarbonates, polystyreneand polyethylene terephthalate (“PET”). The components 38, 40 arepreferably discarded after a single use to make the milling section 14.

The first mold component 38 includes a plunger portion 42 as well as arear portion 44. The second mold component 40 is hollow and presents afront portion 46 and a rear portion 48. The plunger portion 42 of thefirst component 38 and the front portion 46 of the second component 40have matching circular shapes when viewed in reference planesperpendicular to a central axis of the mold assembly 36. The rearportion 44 of the first component 38 and the rear portion 48 of thesecond component 40 have matching, but somewhat larger circular shapeswhen viewed in references planes perpendicular to the central axis ofthe mold assembly 36. (The relative shapes for the portions 42, 44 andthe portions 46, 48 are optional and may be varied according to thedesired diameter of the milling section 14. For example, the portions42, 44 and the portions 46, 48 could have identical cross-sections.)

When the first component 38 is received in the second component 40, theplunger portion 42 slides in the front portion 46 while the rear portion44 slides within the rear portion 48. Preferably, the matching circularshapes of the portions 42, 46 and the matching circular shapes of theportions 44, 48 present a close mating fit so that the first component38 smoothly slides within the second component 40 without undue lateralmovement or “slop”.

As shown in FIG. 5, the second component 40 also includes a cylindricalchannel 50 that is located in the center of the front portion 46. Thechannel 50 leads to an internal mold cavity 52 that is located between afront face of the plunger portion 42 and a front inner wall of the frontportion 46 when the components 38, 40 are assembled together. Thechannel 50 provides an inlet opening for the introduction of restorativematerial into the mold cavity 52 when it is desired to make a millingsection such as the milling section 14 described above.

In use, the components 38, 40 are fully assembled such that the frontface of the plunger 42 initially is closely adjacent, and preferably isin contact with the front wall of the front portion 46. In thisorientation of the components 38, 40, the volume of space in the moldcavity is essentially zero. Next, a quantity of flowable, unhardeneddental restorative material is introduced into the channel 50 and intothe mold cavity 52. As the restorative material is introduced into themold cavity 52, the restorative material pushes against the front faceof the plunger portion 42 and the front, inner wall of the first portion46. The force exerted by the incoming restorative material pushes thecomponents 38, 40 away from each other. If, for example, the secondcomponent 40 is held stationary, the first component 38 moves in arearwardly direction in the second component 40.

As the mold cavity 52 is filled, the flowing restorative materialcontinues to bear against the front face of the plunger portion 42,thereby helping to ensure that air bubbles are not created in the massof restorative material in the mold cavity 52 as the mold cavity 52enlarges in volume. Avoidance of air bubbles in the restorative materialis desired so that the resulting milling section is strong and does notpresent voids that might otherwise appear within or on the surface ofthe resulting prosthetic.

Preferably, back pressure is applied to one or both of the components38, 40 as the mold cavity 52 is filled. If, for example, the secondcomponent 40 is held stationary as mentioned above while the mold cavity52 is filled, pressure is applied to the first component 38 so that thefirst component 38 does not freely move away from the second component40. The back pressure can be applied by use of a piston (of a hydraulicpiston and cylinder assembly) in contact with the outer face of the rearportion 44. Preferably, the amount of pressure applied to the firstcomponent 38 is slightly less than the pumping pressure (i.e., theamount of pressure that is applied to the restorative material in orderto cause the restorative material to flow into the mold cavity 52). Inthis manner, the likelihood of air bubbles in the resulting millingsection is reduced.

In FIG. 6, the restorative material is designated by the numeral 54.FIG. 6 also shows an example of the position of the first component 38relative to the second component 40 after a sufficient amount ofrestorative material has been introduced into the mold cavity 52 to makea milling section. The restorative material in the mold cavity 52 andalso in the channel 54 is then hardened to present a unitary body thatis suitable for use as a milling section, such as the milling section 14described above.

When the restorative material 54 is a polymer-ceramic composite materialas described above and includes a visible light sensitizer, therestorative material 54 is hardened by directing a source of lighttoward the mold cavity 52. For this purpose, the second component 40 andpreferably both of the first and second components 38, 40 are made of atransparent or translucent material that is capable of transmittingactinic radiation. Once the restorative material 54 has sufficientlyhardened, the first component 38 is removed from the second component 40and the resulting milling section is removed from the mold cavity 52 andthe channel 50.

The portion of the hardened restorative material 54 that was previouslyin the channel 50 presents a projection such as the projection 28described above. As a consequence, there is no need to remove theprojection after the molding operation is complete, as might otherwisebe desired to present a flat face for bonding to a flat face of asupport section as known in the prior art. Such a method also avoids theneed for attempting to remove material from the channel 50 beforehardening the material in the mold cavity 52.

The projection 28 is also an advantage during coupling of the supportsection 12 to the milling section 14, in that the projection 28 servesto align the sections 12, 14 to a desired orientation. For example, andin the embodiment described above, if the projection 28 and the recess24 each have a central axis that is collinear with a central axis of theassembly 10, the milling section 14 will be in its desired alignment tothe support section 12 when the two sections 12, 14 are brought togetherfor bonding. In this manner, the likelihood of lateral misplacement ofone of the sections 12, 14 relative to the other during assembly of thesections 12, 14 is reduced.

Once the sections 12, 14 are assembled together, the projection 28functions as a support structure to resist lateral shear forces. Forexample, if a lateral force is applied by a milling tool against themilling section 14, the projection 28 (in combination with the adhesive)helps the assembly 10 in resisting the force so that the milling section14 will remain securely fixed to the support section 12 during theremainder of the milling process (until such time in the process thatdetachment of the support section 12 is desired).

As an additional option, the projection 28 and the recess 24 may beprovided with mating keys and keyways or other structure in order toensure that the support section 12 is in a desired rotational position(i.e., in directions about the central axis of the assembly 10) relativeto the rotational position of the milling section 14. For example, ifthe milling section 14 has a somewhat square configuration in transversecross-section, it may be preferred to align one side of the square tothe position of the notch 22 located on the support section 12. In thismanner, the square configuration of the milling section will be orientedin a certain position relative to the milling machine as may be desired,for example, in order to optimize use of the milling section 14.

As another option, one or more additional projections may be provided.If a plurality of projections are provided, the projections may besymmetrical with respect to the central axis of the assembly 10 oralternatively may be non-symmetrical in order to provide rotationalalignment of the sections 12, 14 as described above. As a furtheroption, the projection or projections could extend from the supportsection and into respective recesses of the milling section. Moreover,projections could extend from both the support section and the millingsection into recesses of the other.

The projection 28 may also have shapes other than that shown in thedrawings. For example, the projections may be in the form of fibers, amachined surface, a mesh surface, a roughened surface or an irregularsurface (such as, for example, may be presented by upstanding shards ofhardened restorative material). As an additional option, the projectionsmay include pores or recesses for bond enhancement. Furthermore, theprojection(s) could have a longitudinal axis that extends perpendicularto the central axis of the assembly, such as one or more projections inthe shape of cross bars that extend across all or a portion of thediameter of the bonding surface 20.

The method of making the milling section 14 may also vary from thatshown in FIGS. 5 and 6. For example, the channel 50 could be eliminatedif desired and one or more recesses could be provided in the front faceof the plunger portion 42 in order to provide space for the restorativematerial to form one or more projections. The restorative material mayalso be introduced through a channel in the first mold component 38 thatoptionally is the same or in communication with the recess mentioned inthe preceding paragraph. Furthermore, the projection or projectionscould be milled or otherwise machined into the milling section after therestorative material is hardened.

A variety of other constructions and methods are also possible and maybe apparent to those skilled in the art. As such, the scope of theinvention should not be deemed limited to the presently preferredembodiments that are described in detail above, but instead only by afair scope of the claims that follow along with their equivalents.

What is claimed is:
 1. A method of making a dental mill blank assemblycomprising the acts of: providing a mold having an inlet channel and amold cavity in communication with the inlet channel; directing aquantity of restorative material along a path that leads through thechannel and into the mold cavity; hardening restorative material locatedin the mold cavity as well as restorative material located in thechannel; removing the hardened restorative material from the mold cavityand the channel; and coupling the hardened restorative material to asupport section, wherein the act of coupling the hardened restorativematerial to a support section includes the act of inserting the portionof the hardened restorative material that was formerly in the channelinto a recess of the support section.
 2. A method of making a dentalmill blank assembly according to claim 1 and including the act ofproviding a quantity of adhesive between the hardened restorativematerial and the support section.
 3. A method of making a dental millblank assembly according to claim 1 wherein the act of inserting theportion of the hardened restorative material that was formerly in thechannel into a recess of the support section is carried out by slidingthe portion of the hardened restorative material into the recess inmating, complemental relation.
 4. A method of making a dental mill blankassembly according to claim 1 wherein the act of providing a mold havingan inlet channel and a mold cavity in communication with the inletchannel includes the act of locating a central axis of the inlet channelin alignment with a central axis of the mold cavity.
 5. A method ofmaking a mill blank assembly according to claim 1 wherein the act ofhardening restorative material located in the mold cavity as well asrestorative material located in the channel is carried out by directinga source of light toward the mold cavity.
 6. A method of making a dentalmill blank assembly comprising the acts of: providing a mold assemblyhaving a first component, a second component and a mold cavity locatedbetween a front face of tile first component and an inner wall of thesecond component; moving the first component and the second componentrelative to each other such that the front face of the first componentis adjacent the inner wall of the second component; directing a quantityof restorative material alone a path that leads through a channel incommunication with the mold cavity and to a location between the frontface of the first component and the inner wall of the second component;introducing the restorative material into the mold cavity under pressuresuch that the restorative material bears against the front face of thefirst component and the inner wall of the second component andrelatively moves the front face and the inner wall away from each other;hardening restorative material located in the mold cavity as well asrestorative material located in the channel; and coupling the hardenedrestorative material to a support section, wherein the act of couplingthe hardened restorative material to a support section includes the actof inserting the portion of the hardened restorative material that wasformerly in the channel into a recess of the support section.
 7. Amethod of making a dental mill blank assembly according to claim 6wherein the act of moving the first component and the second componentrelative to each other such that the front face of the first componentis adjacent the inner wall of the second component includes the act ofcontacting the front face with the inner wall.
 8. A method of making adental mill blank assembly according to claim 6 and including the act ofhardening restorative material located in the mold cavity to make amilling section.
 9. A method of making a dental mill blank assemblyaccording to claim 8 wherein the act of hardening restorative materialin the mold cavity to make a milling section includes the act ofdirecting a source of light toward the mold cavity.
 10. A method ofmaking a dental mill blank assembly according to claim 8 and includingthe act of assembling the milling section to a support section.
 11. Amethod of making a dental mill blank assembly according to claim 6 andincluding the act of applying pressure to at least one of the moldcomponents during at least a portion of the time that restorativematerial is introduced into the mold cavity in order to resist freemovement of the mold components in directions away from each other. 12.A method of making a dental mill blank assembly according to claim 6wherein the act of moving the first component and the second componentrelative to each other includes the act of slidably moving the firstcomponent and the second component relative to each other.
 13. A methodof making a dental mill blank assembly according to claim 6 wherein theact of moving the first component and the second component relative toeach other includes the act of moving the first component and the secondcomponent in telescoping relationship.
 14. A method of making a dentalmill blank assembly according to claim 6 wherein the act of moving thefirst component and the second component relative to each other includesthe act of holding the second component in a stationary position whilemoving the first component into the second component.
 15. A method ofmaking a dental mill blank assembly according to claim 6 and includingthe act of providing a quantity of adhesive between the hardenedrestorative material and the support section.